1. Field of the Invention
The present invention relates to a very high pressure piston pump, with which water, and upon addition of corresponding separating devices, other media as well, can be condensed to pressures in the range of about 22 kbar. Such high pressure piston pumps are now used, especially for water jet cutting by "jet-cutting" processes. Jet-cutting is a very versatile and widely used cutting method, both for very soft and for very hard materials. For example, textiles, corrugated cardboards, plastics, composite fiber materials, and other relatively weak materials can be cut by means of jet-cutting, since, by this method, particularly clean cutting edges of large piles of materials can be attained. One further decisive advantage of this cutting is that only one nozzle needs to be spatially directed and controlled, and no expensive stamping and cutting tools are necessary. Changes in cutting require only one alteration of the control program. With jet-cutting, the cutting of three-dimensional forms is no problem.
2. Description of the Prior Art
The high pressure piston pumps used today for jet-cutting compress the conveying agent, for example, water, to a pressure of about 3000 to 5000 bar. They must be dismantled every 300 to 500 operational hours to replace the piston packings, which are subjected to severe wear. Previously, feed pressures of up to a maximum of 12 kbar could be attained. In such types of highly stressed high pressure piston pumps, the service lives of the high pressure piston packings amount to only about 20 minutes. This limitation determines the present status of jet-cutting. Because of the service life of the high pressure packings, which decreases with increasing feed pressure, the jet-cutting devices used today in industry are only used to a high pressure of about 5 kbar. Intervals of approximately 300 hours between changes of the high pressure piston packings, which are still very short, are a great disadvantage of this cutting technology. Jet-cutting devices are therefore frequently equipped with two high pressure piston pumps, which are alternately operated and serviced. Restrictions on the feed pressure of the currently available jet-cutting devices to about 5 kbar decisively limit the opportunities for their application. Thus, it is not possible, for instance, to effectively and cleanly cut sheet metal or rocks with jet-cutting devices. The use of jet-cutting would be very desirable in cutting sheet metal, since the border areas would not be thermally influenced, as is the case, for example, with laser cutting. Entirely new applications in rock drilling technology may be available through the use of jet-cutting at pressures in the range of 10 kbar and above.
Apart from jet-cutting, such high pressure piston pumps can be used in other areas, such as, for example, in physical chemistry, for determining the characteristics of substances; as catalyst pumps, as pumps for the fretting of pipes; and for other applications.
Ice sealings are fundamentally well known, and are in fact described in the following five patents:
French Patent No. 2,077,144; PA1 French Patent No. 2,038,458; PA1 U.S. Pat. No. 3,333,907; PA1 German Publication No. DE-B 1,229,801; PA1 U.S. Pat. No. 3,612,713.
In all these devices, only pressures, at the most, of a few hundred bar can be sealed. In Swiss Patent No. 640,323, an ice sealing for pressures of over 1000 bar is described. For physical reasons, it is not possible, however, to seal against a pressure higher than 2080 bar. At this pressure, a phase transition takes place in the ice: ice I, with its hexagonal lattice, makes a transition into ice III, with its tetragonal lattice, and the density of the ice is thereby increased by 18 percent. This means that the gap between the piston and cooled casing is increased by about 18 percent. Through the elastic expansion of the casing as the result of the pressure in the conveying space, this gap is likewise increased. Both these parts of the gap expansion cannot be compensated rapidly enough, even with greater cooling, and the seal is broken. Furthermore, the frictional forces arising in this ice sealing are very high in a relatively large range of pressure and piston positions, and therefore make impossible an economical utilization of the same, as demonstrated in ETH-Dissertation number 8015.